The invention relates to the making of filaments and particularly to filament production wherein an elongated rod has a pendant drop formed thereon which is engaged by a rotating heat extractor, such as a copper wheel-like member (e.g. disc).
Even more particularly, the invention relates to the above subject matter wherein filaments are produced from rods of high melting point material, e.g. those having melting points exceeding 1200.degree. Celsius.
With regard to the present invention, the term filament is meant to define slender, elongated metallic elements having a transverse dimension less than the element's length dimension. Examples of such elements include sheet, ribbon, or wire. One particular use for these products is as the combustible fill material within a photoflash lamp such as described in U.S. Pat. Nos. 3,535,063 (L. F. Anderson et al), 3,897,196 (J. P. Saunders et al), and 4,008,040 (D. E. Murray et al), all of which are assigned to the assignee of the present invention. The combustible fill material readily ignites upon activation to provide the intense flash typically associated with photoflash applications. At least two methods are presently used to produce elongated filaments from rods of metallic material. The first involves forming a suspended drop on the end of a vertically oriented rod and engaging the drop from below with a rotating copper disc. Such a process is described in U.S. Pat. No. 3,896,203 (Maringer et al). The disc has a chill surface which has a coefficient of thermal conductivity sufficient to withdraw heat from the molten drop in such rapid fashion so as to form the filamentary element on the surface of the drop. The filament is thereafter emitted and collected for further use.
A second method of producing metallic filaments from rods involves formation of what is termed a sessile drop. By a sessile drop is meant one which is substantially upwardly projected using suitable means to engage a rotating casting disc located above the drop. In other words, the rod and disc are inverted in comparison to the arrangement used in the aforementioned suspended drop process. With regard to the present invention, the term pendant drop will be used and is meant to include both suspended and sessile drops.
One particular problem which occurs in the production of filamentary elements from a pendant drop of molten material concerns the damage (e.g. pits, scratches) which occurs on the casting disc's circumferential edge. The resulting erosion of this surface adversely affects filament release, which results in discontinuity of size and surface configuration of these elements. Additionally, the higher the temperature of the disc's edge, the more rapidly this edge erodes.
From the foregoing background, it can be understood that an apparatus and method which produce dimensionally consistent filaments from a pendant drop of high melting point material and which assure substantial prevention of damage to the circumferential edge of the casting wheel would constitute significant advancements in the art.